Oral administration of nitrous oxide reduces vaso-occlusive pain in mice with sickle cell disease

Male and female Townes transgenic HbSS (sickle) and HbAA (control) mice were used. Only mice that did not exhibit baseline hyperalgesia were used. VOC was evoked by exposing mice to cold ambient temperature (10 degrees C) for 1 hour. This produces vaso-occlusion and robust mechanical and heat hyperalgesia (Khasabova et al., 2022). Mechanical hyperalgesia was defined as a decrease in paw withdrawal threshold (PWT) using calibrated von Frey monofilaments applied to the plantar surface. Heat hyperalgesia was defined as a decrease in paw withdrawal latency (PWL) in response to a radiant heat stimulus applied to the plantar hind paw. PWT and PWL were averaged for both paws. PWT and PWL were determined before and at 10 min after cold exposure. Mice then received vehicle or N2O (HBI-201) by oral gavage (4, 10 or 20 mg/kg body weight), or morphine (5 mg/kg, s.c.), and PWT and PWL were determined at various times thereafter. We also measured oral N2O-mediated analgesia in naïve C57 mice.